Cyclopentadienyl manganese compounds have proven to be excellent antiknocks in gasolines used to operate internal combustion engines. They have been especially beneficial in solving some of the problems present when low-lead or lead-free gasolines are used with internal combustion engines. Use of such compounds as antiknocks is described in U.S. Pat. Nos. 2,818,417, 3,839,552 and 3,127,351, all incorporated herein by reference. It is believed, however by some researchers in the field, that under some operating conditions the presence of certain of these organomanganese antiknocks in some of today's low-lead or lead-free gasoline motor fuels tend, in some manner, not altogether fully understood, to promote or increase the amount of unburned and/or partially oxidized hydrocarbons emitted from an engine which is operated on such a fuel. Thus, a need exists for a method to reduce the amount of unburned or partially oxidized hydrocarbons introduced into the atmosphere from the exhaust gas of an internal combustion engine operating on a lead-free or substantially lead-free gasoline containing, as an antiknock, a cyclopentadienyl manganese antiknock gasoline. The present invention provides a simple effective means of alleviating this problem.
It has been previously suggested that the addition of a cyclic ether to gasoline mixes containing organomanganese antiknocks tends to reduce exhaust hydrocarbon emissions from an internal combustion engine being operated on such a gasoline mix. The addition of one such compound, tetrahydrofuran, to reduce exhaust hydrocarbon emissions is disclosed in recently issued U.S. Pat. No. 4,191,536. It is believed, however, that the particular cyclic ethers of the present invention have not heretofore been disclosed or rendered obvious for use as hydrocarbon emission reducing additives in gasoline containing organomanganese antiknocks. Dioxolane, the preferred exhaust emission reducing additive of the present invention, has previously found use as a solvent in electrochemical cells as typified by U.S. Pat. Nos. 3,990,915, 4,139,681, 4,143,213, 4,166,888, 4,091,191, 4,002,492 and 4,049,879.